Scale modifier for phosphate solutions

ABSTRACT

Disclosed is a composition suitable for phosphatizing metal surfaces wherein an additive is included to modify the properties of the scale which is unavoidably formed on processing equipment. The scale is rendered relatively non-adherent to process equipment surfaces through inclusion of a small quantity of a naphthalene sulfonic acid/formaldehyde condensation product in the treating solution.

United States Patent Smith SCALE MODIFIER FOR PHOSPHATE SOLUTIONS Colin Smith, Brentford, England Oxy Metal Finishing Corporation, Warren, Mich.

Filed: Feb. 4, 1974 Appl. No.: 439,671

Inventor:

Assignee:

Foreign Application Priority Data Feb. 9, 1973 Great Britain 6551/73 US. Cl. 148/22, 148/615 R, 148/615 Z, 252/80 Int. Cl. B23k 35/22, C23f 7/08 Field of Search 148/615 R, 6.15 Z, 6.17, 148/624, 22, 28; 117/161 L; 252/80, 81, 86, 381, 382, 383, 178

References Cited UNlTED STATES PATENTS 3/1968 Trugcsser ct al 106/90 1 Mar. 11, 1975 3,582,376 9/1968 Ames 106/89 Primary ExaminerLeon D. Rosdol Assistant E.raminerCharles R. Wolfe Attorney, Agent, or Firm-Arthur E. Kluegel; Richard P. Mueller; B. F. Claeboe [57] ABSTRACT 3 Claims, N0 Drawings 1 SCALE MODIFIER FOR PHOSPHATE SOLUTIONS BACKGROUND OF THE INVENTION It is well known to form phosphate coatings on metal surfaces by treatment with an acid heavy metal phosphate solution, that is to say by applying to the surfaces an aqueous composition containing heavy metal ions (e.g., Zn, Mn, Mg or Fe) and phosphate ions. One of the chronic problems of such phosphate processes is the buildup of a tightly adherent scale on the apparatus used for storing, heating and applying the phosphate solution, for example on the tank and, especially, on the headers, nozzles and heating elements used. The scale build-up may be so serious as to reduce flow rates and, when application is by spray, may result in changes in the spray pattern, making it difficult to obtain uniform application rate. Scale build-up on heating elements causes insufficient heat exchange and problems in maintaining temperature.

Scale formation originates from various causes. One is that the surface of the metal being treated with the composition is attacked by the composition to result in dissolution of the base metal which then reacts with phosphate to form scale. Another is that the phosphate compositions themselves may tend to dissociate to form scale.

DESCRIPTION OF THE INVENTION where n is a number from 2 to 8 inclusive, and salts thereof.

A particularly preferred material is that sold by Ciba- Geigy (U.K.) Limited under the trademark Belloid, for example Belloid SFD.

The dispersing agent may be used in any amount that is effective to give improved results. The improvement that is obtained in the invention vmost usually is a change in the nature of the deposit that is formed. Thus instead of the deposit being formed as scale which is move the sludge this'cleaning can very easily be effected, for example, by merely rinsing the surfaces carrying the deposit.

Little improvement is obtained if the amount of dispersing agent in the working phosphating solution is less than 0.00055 and it is generally of no further advantage to include more than 0.1%. Best results are usually obtained with amounts of from 0.001 to 0.01% by weight.

The high molecular weight dispersing agent may be included in any aqueous acidic phosphating solution comprising scale forming metal ions and phosphate ions employed in the phosphate coating of metals. The solution may be, for example, a zinc phosphate solution or other coating phosphate solution (e.g., containing Mg, Mn or Fe ions). It may also be a non-coating phosphate solution, e.g., a sodium phosphatesolution. Initially, such non-coating solutions are generally free of scale forming metal ions and scale formation is not then a problem. However, during use iron or other metal ions are generated from the surface being treated to yield an acidic solution containing iron or other scale forming ions such as those of aluminum or zinc. Accordingly, scale formation again becomes a problem, even though the amount of iron may be less than the amount of heavy metal in a coating phosphate solution. Thus, scale formation in both coating and non-coating solutions can be reduced or eliminated by the invention.

The dispersing agent may be included in concentrates, either aqueous or non-aqueous, that are diluted before use to form a working solution or it may be added directly to a working solution.

In addition to including zinc or other metal, e.g., alkali metal ions and phosphate ions, the solution may contain any of the various additives known in the art. The concentration of the various components of the solution will be selected having regard to the end use. For example lighter coatings, and therefore lower concentrations, are required when the coating is to serve as a paint base than when it is only to provide corrosion resistance. Typical concentrations and components for a zinc phosphate solution include the following:

Component Concentration Range Calcium 0 to 100 g/l Zinc l to 50 g/l Nitrate 0 to 250 g/l Phosphate 1 to 100 g/l Sodium 0 to 50 g/l Iron (Fe") 0 to 10 g/l standard methods, for example as described in British tightly adherent, the deposit is formed as an easily re- I movable precipitate or sludge. Thus although the equipment has to be cleaned from time to time to re- Pat. Specifications No. 1296883 or 1297715 and in standard references such as the Metal Finishing Guide Book.

Typically, the metal surface to be treated is washed, rinsed and then has the zinc phosphate solution applied to it, normally by spray or immersion. Conventional further treatment, such as rinsing and drying, may be conducted. Application of the treatment solution is normally carried out at elevated temperatures, for ex- 3 ample 100 to 200F and preferably 130 to 170F. The metal surface treated may be zinc, aluminum, iron (or alloys containing predominant amounts of these).

EXAMPLE A phosphating solution was prepared having the following analysis:

Pointage* 20 Free Acid** 4 P 0.8% N0 0.95% Zn 0.63% Ni 0.00271 Pointage ml of M naOH added to a 10 ml sample to reach the phenolphthalein end point.

"ml of N/IO naOH added to a 10 ml sample to reach the bromo-cresol green end point.

It was applied to steel articles by spray at 65C. It was observed that during use sludge and scale was formed, the scale being tightly adherent and the sludge being difficult to remove.

The process was repeated except that 0.004% of Belloid SFD was included in the solution. It was found that after the same duration of processing substantially the same amount of scale and sludge has been formed but that it was very easy to remove this merely by hosing the apparatus.

What is claimed is:

1. In an aqueous acidic phosphating composition containing scale forming metal ions the improvement 4 4 comprising including at least 0.0005% of'a naphthalene sulfonic acid/formaldehyde condensation product or a salt thereof.

2. The composition of claim 1 wherein the naphthalene sulfonic acid/formaldehyde product has the general formula:

3. The composition of claim 2 wherein said scale forming metal is selected from the group consisting of zinc, manganese, magnesium, iron, aluminum and cal- 

1. IN AN AQUEOUS ACIDIC PHOSPHATING COMPOSITION CONTAINING SCALE FORMING METAL IONS THE IMPROVEMENT COMPRISING INCLUDING AT LEAST 0.0005% OF A NAPHTHALENE SULFONIC ACID/FORMALDEHYDE CONDENSATION PRODUCT OR A SALT THEREOF.
 1. In an aqueous acidic pHosphating composition containing scale forming metal ions the improvement comprising including at least 0.0005% of a naphthalene sulfonic acid/formaldehyde condensation product or a salt thereof.
 2. The composition of claim 1 wherein the naphthalene sulfonic acid/formaldehyde product has the general formula: 